Rechargeable Battery and Electrolysis Method of Making the Same

ABSTRACT

A block or graft copolymer coated lithium metal electrode provides the negative electrode and the solid electrolyte for a rechargeable lithium metal battery that further includes a positive electrode. Optionally, the positive electrode includes elemental sulfur in a conductive matrix. The copolymer coated lithium metal electrode may be manufactured by a process involving electroplating lithium metal through a copolymer coated conductive substrate, for which the copolymer coated conductive substrate has been prepared by coating the conductive substrate in a copolymer solution followed by evaporating the solvent. Alternatively, a lithium metal electrode may be coated directly with copolymer. Rechargeable lithium batteries according to embodiments of the invention have improved cycle life and combustion resistance compared to lithium metal batteries manufactured by conventional methods.

TECHNICAL FIELD

The present invention relates to the manufacture of lithium metalrechargeable batteries using polymeric solid state electrolytes. Theresultant batteries are safer and have increased cycle life compared tolithium metal batteries manufactured by conventional methods.

BACKGROUND ART

Lithium ion batteries (LIBs) dominate the lithium battery market. LIBscontain no metallic lithium present as such. The negative electrodecomprises a carbon host for neutral lithium which is contained therein.In the electrolyte and in the positive electrode lithium is present onlyas the ion. Such batteries are attractive for their high energy densitycompared to that of other rechargeable batteries and for their abilityto operate over multiple charge/discharge cycles. In lithium metalbatteries (LMBs) by contrast the negative electrode comprises metalliclithium, just as in lead-acid batteries the negative electrode comprisesmetallic lead. During discharge of an LMB, lithium metal dissociates toform lithium ions and electrons. The lithium ions migrate through theelectrolyte to the positive electrode. The electrons flow through anexternal circuit where they power a device. As the LMB recharges,lithium ions are reduced back to lithium metal as electrons flow backinto the negative electrode. Because LMBs have intrinsically highercapacity than LIBs, they are the preferred technology for primarybatteries. Moreover, since LMBs can be manufactured in the fully chargedstate, they do not require the lengthy formation process needed for LIBsHowever, poor cycle life, volumetric expansion, and safety concernsrelating to shorts resulting from dendrite formation and the potentialfor violent combustion of the flammable organic electrolytes used inLMBs have limited their practical use as rechargeable batteries.

Lithium metal batteries using sulfur as the positive electrode offerhigher specific capacity than the lithium intercalation compounds thatcurrently dominate the market. However, complex polysulfide speciesproduced upon the reduction of elemental sulfur are soluble in theorganic electrolytes typically used in lithium batteries, resulting inreduced cycle life due to the “polysulfide shuttle” effect.

A novel rechargeable lithium metal battery and methods to produce thesame are needed to improve the cycle life and enhance the safety profileof rechargeable lithium metal batteries, in particular lithium metalbatteries using elemental sulfur in the positive electrode.

SUMMARY OF THE EMBODIMENTS

In accordance with embodiments of the invention, a rechargeable lithiummetal battery is disclosed which includes a negative electrode, thenegative electrode having a conductive substrate coated with a layer oflithium metal, the layer of lithium metal having an inner face and anouter face, the inner face contacting the conductive substrate. Thedisclosed rechargeable lithium metal battery further includes a positiveelectrode. In such embodiments, a lithium ion conductive copolymerfunctional as a solid electrolyte coats the outer face of the lithiummetal on the negative electrode, the lithium ion conductive copolymerhaving microphase separated first domains and second domains, eachdomain above its respective glass transition temperature, T_(g), thefirst domains formed from lithium ion solvating segments and providingcontinuous conductive pathways for the transport of lithium ions and thesecond domains formed from second segments immiscible with the firstsegments, the copolymer being selected from the group consisting of ablock copolymer and a graft copolymer.

In such embodiments, the solid electrolyte is disposed between thenegative electrode and the positive electrode, and is in direct physicalcontact with both the layer of lithium metal and the cathode. Theembodied rechargeable lithium metal battery further includes a lithiumsalt dispersed within the solid electrolyte. In such embodiments thelithium metal battery is configured to interact with an external circuitso that during discharge the layer of lithium metal decreases inthickness, and the copolymer coating conforms its shape to continue tocover the thinning layer of lithium metal, and to accommodate any volumechanges that may occur at the positive electrode. In such embodiments,the lithium metal battery is further configured to interact with theexternal circuit so that during electrolytic recharging voltage appliedacross the external circuit causes the layer of lithium metal to grow inthickness, and the copolymer coating to adjust shape to continue tocover the growing layer of lithium metal, and to accommodate any volumechanges that may occur at the positive electrode.

In some embodiments, the positive electrode of the rechargeable lithiummetal battery includes elemental sulfur. In some embodiments, thelithium ion solvating segments comprise poly(oxyethylene)_(n) sidechains, where n is an integer between 4 and 20. In some embodiments, thecopolymer is a block copolymer. In other embodiments, the copolymer is agraft copolymer.

In some embodiments of the invention, a process is disclosed formanufacturing a lithium metal electrode coated with a lithium ionconductive copolymer, the process including the steps of:

(1) Preparing a coating solution of a lithium salt and a graft or blockcopolymer in a cosolvent, the copolymer having first segments and secondsegments, each segment above its respective glass transitiontemperature, T_(g), the first segments formed from lithium ion solvatinggroups and the second segments being immiscible with the first segments,wherein each segment of the block or graft copolymer is separatelysoluble in the cosolvent.

(2) Coating a first conductive substrate with the coating solution.

(3) Evaporating the cosolvent from the coated conductive substrate sothat the first conductive substrate is coated with a first layer of thelithium ion conductive copolymer, the lithium ion conductive copolymerforming microphase separated first domains and second domains, the firstdomains formed from the first segments and providing continuousconductive pathways for transport of lithium ions and the second domainsformed from the second segments.

(4) Configuring an electrolytic cell with an anode.

(5) Configuring the copolymer coated first conductive substrate as acathode in the electrolytic cell, the electrolytic cell containing alithium salt solution interposed between the anode and the copolymercoated first conductive substrate.

(6) Applying a voltage across the first conductive substrate and theanode, causing a first layer of lithium metal to deposit on the surfaceof the first conductive substrate, sandwiched between the firstconductive substrate and the first layer of lithium ion conductivecopolymer coating, the first layer of lithium ion conductive copolymercoating adjusting shape to continue to cover the growing layer oflithium metal, thereby forming the lithium metal electrode coated withthe first layer of lithium ion conductive copolymer.

In some embodiments, a lithium metal electrode is disclosed that isprepared according to these steps. In some embodiments, during themanufacturing process the contents of the electrolytic cell are coveredby a blanketing atmosphere, the blanketing atmosphere having no morethan 10 ppm of lithium reactive components on a molar basis.

In some embodiments of the process, the anode of the electrodepositioncell is prepared by the additional steps of depositing a second layer oflithium metal on a second conductive substrate coating the second layerof lithium metal with the coating solution evaporating the cosolventfrom the coated second layer of lithium metal so that the second layerof lithium metal is coated with a second layer of lithium ion conductivecopolymer, the lithium ion conductive copolymer forming microphaseseparated first domains and second domains, each domain above itsrespective glass transition temperature, T_(g), the first domains formedfrom the first segments and providing continuous conductive pathways forthe transport of lithium ions and the second domains formed from thesecond segments, thereby obtaining the anode comprising the second layerof lithium metal sandwiched between the second conductive substrate andthe second layer of lithium ion conductive copolymer.

In some embodiments, a lithium metal electrode is disclosed that isprepared according to these additional steps.

In some embodiments, a lithium metal electrode is disclosed that iscoated with a lithium ion conductive copolymer that is a blockcopolymer. In some embodiments, a lithium metal electrode is disclosedthat is coated with a lithium ion conductive copolymer that is a graftcopolymer.

In some embodiments, the lithium ion conductive copolymer has segmentswith poly(oxyethylene)_(n) side chains, where n is an integer between 4and 20. In some such embodiments, the lithium ion conductive copolymerfurther has segments of poly(alkyl methacrylate). In the copolymer eachsegment is above its respective glass transition temperature, T_(g).

In some embodiments, the lithium conductive copolymer is a graftcopolymer with main chain segments including poly(oxyethylene)_(n) sidechains, where n is an integer between 4 and 20, and branch segmentsincluding poly(dimethyl siloxane).

In some embodiments, the lithium ion conductive copolymer ispoly[(oxyethylene)₉ methacrylate]-b-poly(butyl methacrylate)(POEM-b-PBMA). In some such embodiments, the ratio of POEM to PBMA isbetween 55:45 and 70:30 on a molar basis. In some embodiments, thelithium ion conductive copolymer is poly[(oxyethylene)₉methacrylate]-g-poly(dimethyl siloxane).

In some embodiments, a process is disclosed for manufacturing a lithiummetal electrode that includes the steps of:

Inserting a first conductive substrate as a cathode in an electrolyticcell.

Inserting a second conductive substrate coated with lithium metal as ananode in the electrolytic cell.

Providing a lithium ion conducting copolymer separating and surroundingthe first conductive substrate and the anode, the lithium ion conductivecopolymer being a graft or block copolymer with first segments andsecond segments, the first segments formed from lithium ion solvatinggroups and the second segments being immiscible with the first segments.

Applying a voltage across the conductive substrate and the anode,causing lithium metal to deposit on the surface of the first conductivesubstrate, the lithium ion conductive copolymer adjusting shape to covera growing layer of lithium metal on the first conductive substrate, anda thinning layer of lithium metal on the second conductive substrate,thereby forming the lithium metal electrode comprising the firstconductive substrate and the lithium metal coating the first conductivesubstrate, wherein the lithium metal on the first conductive substrateis more pure than the lithium metal on the second conductive substrate.

According to some embodiments of the invention, a rechargeable lithiummetal battery is disclosed that includes a positive electrode and anegative electrode, the negative electrode having a layer of lithiummetal coated with a layer of lithium ion conductive copolymer, whereinthe lithium ion conductive copolymer is disposed between the negativeelectrode and the positive electrode, and is in direct physical contactwith both the layer of lithium metal and the positive electrode.According to such embodiments, the lithium metal battery is configuredso that during discharge the layer of lithium metal decreases inthickness, and the copolymer coating conforms its shape to continue tocover the thinning layer of lithium metal. Further, according to suchembodiments, the lithium metal battery is configured so that duringelectrolytic recharging the layer of lithium metal grows in thickness,and the copolymer coating conforms its shape to continue to cover thegrowing layer of lithium metal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of embodiments will be more readily understood byreference to the following detailed description, taken with reference tothe accompanying drawings, in which:

FIG. 1 illustrates the structural features of block and graftcopolymers.

FIG. 2 shows steps in manufacturing a rechargeable lithium metal batterywith a copolymer coated lithium negative electrode according toembodiments of the invention.

FIG. 3a provides a cross-sectional view of a copolymer coated conductivesubstrate prior to electroplating lithium metal onto the substrateaccording to embodiments of the invention.

FIG. 3b provides a top view of a copolymer coated conductive substrateprior to electroplating lithium metal onto the substrate according toembodiments of the invention.

FIG. 4a provides a cross-sectional view of the conductive substrate ofFIGS. 3a and 3b after electroplating lithium metal onto the substrate toform a lithium metal layer sandwiched between the conductive substrateand the copolymer coating according to embodiments of the invention.

FIG. 4b provides a top view of the conductive substrate of FIG. 4aaccording to embodiments of the invention.

FIG. 5a provides a cross-sectional view of a lithium metal coatedconductive substrate prior to coating with copolymer according toembodiments of the invention.

FIG. 5b provides a top view of a lithium metal coated conductivesubstrate prior to coating with copolymer according to embodiments ofthe invention.

FIG. 6a provides a cross-sectional view of the lithium metal coatedconductive substrate of FIGS. 5a and 5b after coating with copolymeraccording to embodiments of the invention.

FIG. 6b provides a top view of the lithium metal coated conductivesubstrate of FIGS. 5a and 5b after coating with copolymer according toembodiments of the invention.

FIG. 7 shows an electrolytic cell suitable for manufacturing thecopolymer coated lithium metal electrode according to embodiments of theinvention, prior to electroplating of lithium onto the conductivesubstrate. In this cell the lithium salt solution is replenished by theflow of lithium salt solution into the cell.

FIG. 8 shows the electrolytic cell of FIG. 7 following electroplating oflithium onto the conductive substrate.

FIG. 9 shows an electrolytic cell suitable for manufacturing thecopolymer coated lithium metal electrode according to embodiments of theinvention, prior to electroplating of lithium onto the conductivesubstrate. In this cell lithium ion in the lithium salt solution isreplenished by oxidation of lithium at the lithium positive electrode.

FIG. 10 shows the electrolytic cell of FIG. 9 following electroplatingof lithium onto the conductive substrate.

FIG. 11 shows an electrolytic cell with a copolymer solid electrolytesuitable for electroplating lithium metal onto a conductive substrateaccording to embodiments of the invention.

FIG. 12 shows the electrolytic cell of FIG. 11 following electroplatingof lithium metal onto the conductive substrate.

FIG. 13 shows a cross-section of a rechargeable battery constructed withthe copolymer coated lithium metal electrode according to an embodimentof the invention. The battery in this embodiment includes a singlepositive electrode.

FIG. 14 shows a cross-section of a rechargeable battery constructed withthe copolymer coated lithium metal electrode according to an embodimentof the invention. The battery in this embodiment includes two positiveelectrodes.

FIG. 15 shows an exterior view of the rechargeable battery embodied inFIG. 11.

FIG. 16 shows an exterior view of the rechargeable battery embodied inFIG. 12.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Definitions. As used in this description and the accompanying claims,the following terms shall have the meanings indicated, unless thecontext otherwise requires:

A “solid electrolyte” is solid material at room temperature which allowsion transport between electrodes of an electrolytic or galvanic cell.

A “block copolymer” is a polymer with blocks made up of one monomeralternating with blocks of another monomer along a linear polymerstrand.

A “graft copolymer” is a polymer which has a backbone strand made up ofone type of monomer and branches of a second monomer.

A “segment” is a block for a block copolymer and a side chain orbackbone for a graft copolymer.

“Microphase separation” of a block or graft copolymers occurs whenpolymer segments segregate into domains according to their monomericunits.

A “cosolvent” for different monomers is a solvent capable of dissolvingeach of the different segments of a block or graft copolymer.

A “common solvent” is identical with a “cosolvent.”

A “negative electrode” functions as an anode in a galvanic cell and as acathode in an electrolytic cell.

A “positive electrode” functions as a cathode in a galvanic cell and asan anode in an electrolytic cell.

The tendency for lithium metal batteries to form dendrites can lead toelectrical shorting. The common use of flammable organic electrolytesfor such batteries exacerbates the potential of such shorts to lead tofires and explosions. Solid electrolytes have potential for eliminatingthese safety concerns by reducing dendrite formation and by avoiding theuse of flammable organic electrolytes.

The ideal solid electrolyte has the ion transport properties of aliquid, the ability to preferentially transport desired ionic species,while blocking the transport of undesirable species. The ideal solidelectrolyte has low flammability, and a resistance to dendriteformation. The ideal solid electrolyte has the mechanical properties ofa solid, but can undergo molecular rearrangements to grow, to shrink,and to accommodate volume changes associated with positive and negativeelectrodes while still maintaining physical contact with both positiveand negative electrodes.

Lithium sulfur (Li—S) batteries using sulfur as the positive electrodeoffer higher specific capacity than the lithium intercalation compoundsthat currently dominate the market. However, complex polysulfide speciesproduced upon the reduction of elemental sulfur dissolve in the organicelectrolytes typically used in lithium batteries, resulting in reducedcycle life due to the “polysulfide shuttle” effect.

Consequently, another desirable feature of a solid electrolyte forlithium metal batteries is the ability to block the “polysulfideshuttle” between the positive and negative electrodes that reducesbattery performance and cycle life of Li—S batteries.

As illustrated in FIG. 1, block copolymers 5 of embodiments of theinvention have alternating blocks of monomer units, here designated bytype “A” and type “B” monomers. In contrast graft copolymers 15embodiments have a backbone made up of type “A” monomers and side-chainsof type “B” monomers. The block copolymer 5 of FIG. 1 is a di-blockpolymer (AB) with one block of A and one block of B. In otherembodiments, block copolymers can be tri-block (ABA or BAB) ormulti-block copolymers.

Block copolymers with blocks of immiscible groups and graft copolymerswith immiscible backbone and side-chain segments as embodied in thisapplication provide a solid electrolyte with the ion transportproperties of a liquid, and with the ability to preferentially transportdesired ionic species, while blocking the transport of undesirablespecies. The thus embodied solid electrolyte has low flammability, and aresistance to dendrite formation. The thus embodied solid electrolytehas the mechanical properties of a solid, but can undergo molecularrearrangements to grow, to shrink, and to accommodate volume changesassociated with positive and negative electrodes while still maintainingphysical contact with both positive and negative electrodes.

Consequently, block copolymers with blocks of immiscible groups andgraft copolymers with immiscible backbone and side-chain segments asembodied in this application provide a solid electrolyte technology forlithium metal batteries in general and Li—S batteries in particular,promising improved safety and performance, longer battery life, and asolution to the “polysulfide shuttle” problem. In short, blockcopolymers and graft copolymers as embodied in this application providethe key features of an ideal solid electrolyte for lithium metalbatteries.

A block or graft copolymer as embodied in this application has one ormore “A” segments of more hydrophilic lithium salt solvating polymersinterspersed with one or more “B” segments of more hydrophobic polymers.All segments are above their respective glass transition temperatures,T_(g). Material incorporating such a block or graft copolymer willmicrophase separate into locally segregated nanoscale domains of “A” and“B” segments. The resultant ordering of segments in turn confersconformational rigidity to the material even though all of theconstituents are segmentally liquid. For suitable A:B ratios, the Asegments form continuous lithium ion solvating channels. For lithium ionsolvating segments having suitably high local chain mobility, highlithium conductivity allows the directed flow of lithium ions throughthe copolymer upon application of an electric field.

Dissolving the block or graft copolymer and a lithium salt in a suitablecommon solvent (cosolvent) that is capable of dissolving both A and Bsegments allows ready processing of the polymer with solvated lithiumions by conventional coating methods. For example, electrodes can bedirectly coated with a lithium ion conductive block or graft copolymerelectrolyte by dipping the electrode in a solution of lithium salt andcopolymer dissolved in cosolvent, and allowing the cosolvent toevaporate. Such an electrode can then be directly used in a battery orelectrolytic cell. In this manner, as described below, lithium metalelectrodes can be coated with lithium ion conducting block or graftcopolymer solid electrolytes for use in solid state batteries.

Suitable copolymers can be di-block copolymers (AB), tri-blockcopolymers (ABA or BAB), or higher multiblock polymers with alternatingA and B blocks. All blocks are above their respective glass transitiontemperatures, T_(g). Likewise suitable are graft copolymers withbackbone A monomers and side-chain B monomers, or back-bone B monomersand side-chain A monomers. In some embodiments, the A segmentsincorporate short poly(oxyethylene)_(n) side chains, where n, the numberof oxyethylene groups in the side chain ranges from 4 to 20, preferablybetween 7 and 11. In some embodiments n is equal to nine. In someembodiments the poly(oxyethylene)_(n) side chains are incorporated bypolymerization of poly(oxyethylene)_(n) methacrylate monomers. In apreferred embodiment, the A segments are synthesized by polymerizationof poly(oxyethylene)₉ methacrylate monomers.

In some embodiments, the B segments have alkyl side chains having from 3to 6 carbons. In some embodiments, the B segments are synthesized from apoly(alkyl methacrylate). In some embodiments, the poly(alkylmethacrylate) is chosen from the group consisting of poly(propylmethacrylate), poly(butyl methacrylate), poly(pentyl methacrylate), andpoly(hexyl methacrylate). In a preferred embodiment, the poly(alkylmethacrylate) is poly(butyl methacrylate).

In some embodiments the “A” segments incorporate a mixture of neutraland anionic groups. In some such embodiments, the anionic groups areconfigured in order to minimize coordination of the anionic groups withlithium cations.

In a particularly preferred embodiment, the copolymer is the di-blockcopolymer poly[(oxyethylene)₉ methacrylate]-b-poly(butyl methacrylate)(POEM-b-PBMA).

In some embodiments, the block copolymers are synthesized by livinganionic polymerization. In some embodiments, the block copolymers aresynthesized by atom transfer radical polymerization (ATRP).

In some embodiments, the copolymer is a graft copolymer with ahydrophilic backbone of “A” segments that are lithium salt solvating andhydrophobic side-chains of “B” segments made up of hydrophobic polymers.Each segment is above its respective glass transition temperature,T_(g).

In a preferred embodiment, the copolymer is a graft copolymer withbackbone “A” segments incorporating short poly(oxyethylene)_(n) sidechains, where n, the number of oxyethylene groups in the side chainranges from 4 to 20, preferably between 7 and 11. In some embodiments, nis equal to nine. In some embodiments, the poly(oxyethylene)_(n) sidechains are incorporated by polymerization of poly(oxyethylene)_(n)methacrylate monomers. In a preferred embodiment, the A segments aresynthesized by polymerization of poly(oxyethylene)₉ methacrylatemonomers.

In some embodiments, the polymer is a graft copolymer with side chain“B” segments incorporating poly(dimethyl siloxane) (PDMS). In apreferred embodiment, the graft copolymer is incorporated into apoly(oxyethylene)_(n) methacrylate backbone by random copolymerizationof poly(dimethyl siloxane) monomethacrylate macromonomer (PDMSMA) withpoly(oxyethylene)_(n) methacrylate monomers to form a graft copolymer oftype POEM-g-PDMS. In preferred embodiments, poly(oxyethylene)₉methacrylate monomers are reacted to form the POEM-g-PDMS copolymer.

In some embodiments, the “A” backbone includes additional monomers. Insome embodiments the additional monomers are anionic. In an embodiment,poly(oxyethylene)₉ methacrylate monomers are copolymerized withmethacrylate monomers (MAA) and with PDMSMA to formpoly(oxyethylene)₉-ran-MAA-g-PDMS. In a preferred embodiment, thecarboxylic acid groups of this polymer are reacted with BF₃ to giveanionic boron trifluoride esters, which have a reduced tendency tocomplex lithium ions when compared with MAA carboxylate groups.

As summarized by the manufacturing steps shown in FIG. 2, in someembodiments, a copolymer coated lithium metal electrode is manufacturedand inserted into a cell to function as a negative electrode (the metal)and a solid electrolyte (the polymer) in a lithium metal battery.

The steps of this embodiment are as follows: First, prepare a solutionof lithium ion salt and block or graft copolymer in a cosolvent capableof dissolving both A and B segments of the copolymer 2. Second, coat anelectrically conductive substrate with lithium salt doped copolymer bydipping the substrate in the lithium salt and copolymer solution 4.Third, evaporate the cosolvent to leave the electrolytically conductivesubstrate coated with lithium ion conductive copolymer 6. Next, insertthe lithium ion conductive copolymer-coated conductive substrate as acathode in an electrolytic cell, the electrolytic cell including ananode and a lithium salt solution 8. Then, apply voltage across theanode and the substrate, acting as a cathode, causing electrons to flowfrom the anode through an external circuit to the conductive substrate,causing lithium ions to be pulled through the copolymer coating, to bereduced at the substrate surface, thereby electrolytically platinglithium metal onto the surface 10. As lithium metal plates, the polymerchains of the copolymer coating undergo a molecular rearrangement,allowing the copolymer coating to continue to cover the growing layer oflithium metal, resulting in a final product for which the substrate iscoated with a layer of lithium metal, and the layer of lithium metal isin turn coated with a layer of copolymer solid electrolyte. In the finalstep, the conductive substrate layered with lithium metal and acopolymer solid electrolyte is inserted as the combined lithium metalnegative electrode and solid electrolyte in a lithium metal battery 12.

FIG. 3a shows a cross-section and FIG. 3b shows a top view of acopolymer coated electrically conductive substrate 115 according toembodiments of the invention. Following the process of dipping theelectrically conductive substrate 110 into a cosolvent solution oflithium salt and copolymer and drying, the centrally locatedelectrically conductive substrate 110 is surrounded by a layer ofcopolymer solid electrolyte 160. FIG. 4a shows a cross-section and FIG.4b shows a top view of the copolymer coated lithium metal electrode 116that can be obtained following the electrolytic plating onto theelectrically conductive substrate 110 of a layer of lithium metal 150which fills the space between the conductive substrate 110 and thecopolymer solid electrolyte 160.

In the embodiment shown in FIGS. 5a, 5b, 6a, and 6b , the copolymercoated lithium metal electrode 116 can be obtained by first preparing,by electroplating or by other means, a lithium plated conductivesubstrate 117, then dipping the lithium plated substrate in a cosolventsolution of copolymer and drying the lithium plated substrate to obtaina copolymer coated negative electrode 115. FIG. 5a shows a cross-sectionand FIG. 5b shows a top view of a lithium coated conductive substrate117 prior to coating with the copolymer solid electrolyte 160. FIG. 6ashows a cross-section and FIG. 6b shows a top view of the copolymercoated lithium metal electrode 116 after coating the lithium coatedconductive substrate 117 with the copolymer solid electrolyte.

In preferred embodiments, the lithium metal in the copolymer coatedlithium metal electrode 116 is ultrapure, having no more than five ppmof non-metallic elements by mass. In some embodiments, the lithium metalin the copolymer coated lithium metal electrode 116 includes no morethan one ppm of non-metallic elements by mass. In some embodiments thelithium coated conductive substrate 117 is manufactured by methodsdescribed in U.S. patent application Ser. Nos. 17/006,048 and17/006,073, both of which were filed Aug. 28, 2020 and are incorporatedby reference herein in their entirety.

In preferred embodiments, the conductive substrate is selected from thegroup consisting of copper, aluminum, graphite coated copper, andnickel. In some embodiments, the copolymer is (POEM-b-PBMA). In someembodiments, the ratio of POEM to PBMA is greater than 50:50 on a molarbasis. In preferred embodiments, the ratio of POEM to PBMA is between55:45 and 70:30 on a molar basis. In a preferred embodiment, thecosolvent is tetrahydrofuran (THF).

An embodiment of an electrolytic cell 105 for electroplating theelectrically conductive substrate 110 with a layer of lithium metal 150sandwiched between the conductive substrate 110 and the copolymercoating 160 is shown in FIG. 7 (before electroplating) and FIG. 8 (afterelectroplating). In manufacturing the copolymer coated lithium metalelectrode 116, the copolymer coated electrically conductive substrate115 is positioned as the cathode in the electrolytic cell 105. As shownin FIG. 7, the electrolytic cell 105 contains an anode 120 and a lithiumsalt solution 140 in contact with the anode 120 and with the copolymer160 coating the conductive substrate 110.

In some embodiments, the electrolytic cell 105 is configured as a flowchamber, with an entrance port 170 and an exit port 180 allowing lithiumsalt solution 140 to enter the electrolytic cell 105 to provide arenewable supply of lithium ions for electroplating. In someembodiments, the electrolytic cell is completely blanketed with ablanketing atmosphere 124, the blanketing atmosphere being substantiallyfree of lithium reactive components. In a preferred embodiment, theblanketing atmosphere includes no more than 10 ppm of lithium reactivecomponents on a molar basis. In a preferred embodiment, the blanketingatmosphere includes no more than 5 ppm of lithium reactive components ona molar basis. In a preferred embodiment, the blanketing atmosphereincludes no more than 10 ppm of nitrogen on a per molar basis. In apreferred embodiment, the blanketing atmosphere includes no more than 5ppm of nitrogen on a per molar basis. In a preferred embodiment, theblanketing atmosphere includes no more than 1 ppm of nitrogen on a permolar basis. In a preferred environment, the blanketing atmospherecomprises argon with a purity of greater than 99.998 weight percent. Ina preferred embodiment the blanketing atmosphere 124 and theelectrolytic cell 105 are enclosed in a gas-impermeable container 500.

As shown in FIG. 8, in some embodiments, during electroplating a voltageis applied across the anode 120 and the conductive substrate 110 of theelectrolytic cell 105, causing electrons to flow through an externalcircuit to the conductive substrate 110 and pulling lithium ions fromthe lithium salt solution 140 through the copolymer 160 to plate ontothe surface of the conductive substrate, forming a layer of lithiummetal 150 sandwiched between the conductive substrate 110 and thecopolymer 160. As the layer of lithium metal 150 grows, the copolymer160 undergoes molecular rearrangement, maintaining contact with thesurface of the layer of lithium metal 150. In the process, a copolymercoated lithium metal electrode 116 is manufactured.

As shown in FIGS. 9 and 10, in some embodiments, the electrolytic cell105 includes a negative electrode comprising a first conductivesubstrate 110 coated with copolymer 160, to be electroplated with afirst layer of lithium metal 150, and a positive electrode 120 with asecond conductive substrate 112 in physical contact with a second layerof lithium metal 155, the second layer of lithium metal 155 coated withcopolymer 165. As voltage is applied across the electrodes, the secondlayer of lithium metal 155 releases lithium ions through the copolymercoating into the lithium salt solution 145, replenishing the supply oflithium ions as electroplating of lithium metal occurs on the surface ofthe first conductive substrate 110. Consequently, as shown in FIG. 10,as the layer of lithium metal 150 sandwiched between the firstconductive substrate 110 and the copolymer 160 increases in thickness,the second layer of lithium metal 155 sandwiched between the secondconductive substrate 112 and the copolymer 165 decreases in thickness.

In the embodiment of FIGS. 11 and 12, an electrolytic cell 105 includesa first conductive substrate 110 functioning as a cathode, and an anodemade of a second conductive substrate 112 coated with impure lithium155. Separating and surrounding the two electrodes is a lithium ionconducting copolymer 160. Lithium salt is dispersed in the lithium ionconducting copolymer. As voltage is applied across the electrodes,electrons flow through an external circuit from the second conductivesubstrate to the first conductive substrate 110, causing the secondlayer of lithium metal 155 to release lithium ions, which flow throughthe lithium ion conducting copolymer 160 to the first conductivesubstrate, where they are reduced, electroplating lithium metal 150 onthe surface of the first conductive substrate 110. Consequently, asshown in FIG. 12, as the first layer of lithium metal 150 on the firstconductive substrate 110 increases in thickness, the second layer oflithium metal on the second conductive substrate 112 decreases inthickness. As lithium metal leaves the anode and travels to the cathode,the lithium ion conducting copolymer undergoes molecular rearrangementto maintain contact with the first layer of lithium metal 150 and secondlayer of lithium metal 155.

An advantage of the embodiments of FIGS. 9-12 is that the electroplatedfirst layer of lithium metal 150 will be of higher purity and will havea smoother surface than the electroplating second layer of lithium metal155. The method thus provides a straightforward means of obtaininghigher purity, microscopically smoother lithium metal electrodes to usein lithium metal batteries, starting with lower purity, microscopicallyrougher lithium metal.

The copolymer coated lithium metal electrode 116, prepared byelectrolytic or other methods, can be inserted directly into arechargeable lithium battery, shown in cross-section in FIGS. 13 and 14,with exterior views in FIGS. 15 and 16, respectively.

In the battery embodied in FIGS. 13 and 15, a single positive electrode130 is directly juxtaposed against the outer layer of copolymer 160coating the negative electrode, to form a rechargeable battery 170 withthe copolymer 160 providing the solid state electrolyte.

In the battery embodied in FIGS. 14 and 16, two positive electrodes 130are directly juxtaposed against two sides of the outer layer ofcopolymer 160 coating the negative electrode, to form a rechargeablebattery 175 with the copolymer 160 providing the solid stateelectrolyte.

In preferred embodiments of the batteries of FIGS. 13-16, a lithium saltis dispersed within the copolymer. In some embodiments, the lithium saltis LiCF₃SO₃. In some embodiments LiCF₃SO₃ is dispersed within thecopolymer at a molar ratio of between 50:1 and 10:1 ethylene oxide tolithium ion. In a preferred embodiment, the LiCF₃SO₃ is dispersed withinthe copolymer at a molar ratio of 20:1 ethylene oxide to lithium ion. Insome embodiments, the copolymer with dispersed lithium salt coating thenegative electrode is formed by solution casting directly from anhydrousTHF.

In some embodiments the rechargeable batteries of FIGS. 13-16 are Li—Sbatteries, for which the positive electrode includes elemental sulfur.In preferred embodiments, the sulfur in the positive electrode isassociated with a conductive matrix, enabling suitably high electronconductivity.

Li—S batteries constructed in the manner of FIGS. 13-16 enable Li⁺transport, but block the transport of anions, including in particularpolysulfide anions. Consequently, the polysulfide shuttle responsiblefor reducing the performance and cycle life of Li—S batteries isvitiated.

The embodiments of the invention described above are intended to bemerely exemplary; numerous variations and modifications will be apparentto those skilled in the art. All such variations and modifications areintended to be within the scope of the present invention as defined inany appended claims.

What is claimed is:
 1. A rechargeable lithium metal battery comprising:a negative electrode, the negative electrode having a conductivesubstrate coated with a layer of lithium metal, the layer of lithiummetal having an inner face and an outer face, the inner face contactingthe conductive substrate; a positive electrode; a solid electrolytecomprising a lithium ion conductive copolymer coating the outer face ofthe lithium metal, the lithium ion conductive copolymer havingmicrophase separated first domains and second domains, each domain aboveits respective glass transition temperature, T_(g), the first domainsformed from lithium ion solvating segments and providing continuousconductive pathways for the transport of lithium ions and the seconddomains formed from second segments immiscible with the first segments,the copolymer being selected from the group consisting of a blockcopolymer and a graft copolymer; and a lithium salt dispersed within thesolid electrolyte; wherein the solid electrolyte is disposed between thenegative electrode and the positive electrode, and is in direct physicalcontact with both the layer of lithium metal and the cathode, whereinthe lithium metal battery is configured to interact with an externalcircuit so that during discharge: the layer of lithium metal decreasesin thickness, and the copolymer coating conforms its shape to continueto cover the thinning layer of lithium metal, and to accommodate anyvolume changes that may occur at the positive electrode, wherein thelithium metal battery is configured to interact with the externalcircuit so that during electrolytic recharging: a voltage applied acrossthe external circuit causes the layer of lithium metal to grow inthickness, and the copolymer coating to adjust shape to continue tocover the growing layer of lithium metal, and to accommodate any volumechanges that may occur at the positive electrode.
 2. The rechargeablelithium metal battery of claim 1 wherein the positive electrodecomprises elemental sulfur.
 3. The rechargeable lithium metal battery ofclaim 1 wherein the lithium ion solvating segments comprisepoly(oxyethylene)_(n) side chains, where n is an integer between 4 and20.
 4. The rechargeable lithium metal battery of claim 1 wherein thecopolymer is a block copolymer.
 5. The rechargeable lithium metalbattery of claim 1 wherein the copolymer is a graft copolymer.
 6. Aprocess for manufacturing a lithium metal electrode coated with alithium ion conductive copolymer, comprising: preparing a coatingsolution of a lithium salt and a block or graft copolymer in acosolvent, the copolymer having first segments and second segments, eachsegment above its respective glass transition temperature, T_(g), thefirst segments formed from lithium ion solvating groups and the secondsegments being immiscible with the first segments, wherein each segmentof the block or graft copolymer is separately soluble in the cosolvent;coating a first conductive substrate with the coating solution;evaporating the cosolvent from the coated conductive substrate so thatthe first conductive substrate is coated with a first layer of thelithium ion conductive copolymer, the lithium ion conductive copolymerforming microphase separated first domains and second domains, the firstdomains formed from the first segments and providing continuousconductive pathways for transport of lithium ions and the second domainsformed from the second segments; configuring an electrolytic cell withan anode; configuring the copolymer coated first conductive substrate asa cathode in the electrolytic cell, the electrolytic cell containing alithium salt solution interposed between the anode and the copolymercoated first conductive substrate; applying a voltage across the firstconductive substrate and the anode, causing a first layer of lithiummetal to deposit on the surface of the first conductive substrate,sandwiched between the first conductive substrate and the first layer oflithium ion conductive copolymer coating, the first layer of lithium ionconductive copolymer coating adjusting shape to continue to cover thegrowing layer of lithium metal, thereby forming the lithium metalelectrode coated with the first layer of lithium ion conductivecopolymer.
 7. The process according to claim 6, wherein the anode isprepared by a process comprising: depositing a second layer of lithiummetal on a second conductive substrate; coating the second layer oflithium metal with the coating solution; evaporating the cosolvent fromthe coated second layer of lithium metal so that the second layer oflithium metal is coated with a second layer of lithium ion conductivecopolymer, the lithium ion conductive copolymer forming microphaseseparated first domains and second domains, the first domains formedfrom the first segments and providing continuous conductive pathways fortransport of lithium ions and the second domains formed from the secondsegments, thereby obtaining the anode comprising the second layer oflithium metal sandwiched between the second conductive substrate and thesecond layer of lithium ion conductive copolymer.
 8. A lithium metalelectrode coated with lithium ion conductive copolymer manufacturedaccording to the process of claim
 6. 9. A lithium metal electrode coatedwith lithium ion conductive copolymer manufactured according to theprocess of claim
 7. 10. The lithium metal electrode coated with lithiumion conductive copolymer according to claim 8, wherein the lithium ionconductive copolymer is a block copolymer.
 11. The lithium metalelectrode coated with a lithium ion conductive copolymer according toclaim 8, wherein the lithium ion conductive copolymer is a graftcopolymer.
 12. The lithium metal electrode coated with a lithium ionconductive copolymer according to claim 8, wherein the first segmentscomprise poly(oxyethylene)_(n) side chains, where n is an integerbetween 4 and
 20. 13. The lithium metal electrode coated with a lithiumion conductive copolymer according to claim 12, wherein the secondsegments comprise poly(alkyl methacrylate).
 14. The lithium metalelectrode coated with lithium ion conductive copolymer according toclaim 12, wherein the second chains comprise poly(dimethyl siloxane).15. The lithium metal electrode coated with lithium ion conductivecopolymer according to claim 8, the lithium ion conductive copolymerbeing poly[(oxyethylene)₉ methacrylate]-b-poly(butyl methacrylate)(POEM-b-PBMA).
 16. The lithium metal electrode coated with lithium ionconductive copolymer according to claim 8, the lithium ion conductivecopolymer being poly[(oxyethylene)₉ methacrylate]-g-poly(dimethylsiloxane).
 17. The lithium metal electrode coated with lithium ionconductive copolymer according to claim 15, wherein the ratio of POEM toPBMA is between 55:45 and 70:30 on a molar basis.
 18. The lithium metalelectrode coated with a lithium ion conductive copolymer according toclaim 8, wherein during the manufacturing process the contents of theelectrolytic cell are covered by a blanketing atmosphere, the blanketingatmosphere having no more than 10 ppm of lithium reactive components ona molar basis.
 19. A process for manufacturing a lithium metal electrodecomprising: inserting a first conductive substrate as a cathode in anelectrolytic cell; inserting a second conductive substrate coated withlithium metal as an anode in the electrolytic cell; providing a lithiumion conducting copolymer separating and surrounding the first conductivesubstrate and the anode, the lithium ion conductive copolymer being agraft or block copolymer with first segments and second segments, eachsegment above its respective glass transition temperature, T_(g), thefirst segments formed from lithium ion solvating groups and the secondsegments being immiscible with the first segments; applying a voltageacross the conductive substrate and the anode, causing lithium metal todeposit on the surface of the first conductive substrate, the lithiumion conductive copolymer adjusting shape to cover a growing layer oflithium metal on the first conductive substrate, and a thinning layer oflithium metal on the second conductive substrate, thereby forming thelithium metal electrode comprising the first conductive substrate andthe lithium metal coating the first conductive substrate, wherein thelithium metal on the first conductive substrate is more pure than thelithium metal on the second conductive substrate.
 20. A rechargeablelithium metal battery comprising: a positive electrode and a negativeelectrode, the negative electrode having a layer of lithium metal coatedwith a layer of lithium ion conductive copolymer, the negative electrodemanufactured according to the process of claim 6, wherein the lithiumion conductive copolymer is disposed between the negative electrode andthe positive electrode, and is in direct physical contact with both thepositive electrode and the layer of lithium metal, wherein the lithiummetal battery is configured so that during discharge: the layer oflithium metal decreases in thickness, and the copolymer coating conformsits shape to continue to cover the thinning layer of lithium metal,wherein the lithium metal battery is configured so that duringelectrolytic recharging: the layer of lithium metal grows in thickness,and the copolymer coating conforms its shape to continue to cover thegrowing layer of lithium metal.